The present application is related to a low leakage group III-nitride semiconductor structure which is ideally suited for use in high voltage, high frequency or high temperature electronic devices. More specifically, the present invention is related to an aluminum indium nitride and aluminum indium gallium nitride semiconductor device which has low leakage and improved properties.
Group III nitrides have attracted a significant amount of attention for use in a variety of semiconductor applications due, in part, to their wide and direct band gaps. Devices utilizing group III nitrides enjoy a relatively high break down voltage and a high saturated electron mobility.
Group III-Nitride based High Electron Mobility Transistors (HEMT), show tremendous promise as switching elements for power electronic applications. The key requirements for high power switches include high breakdown voltages (VBR), minimum conduction and switching losses and high switching frequency which allows them to cope with modern trends in power converter-inverter, design and to allow monolithically integrated power converter technology.
One of the widely known Group III-nitride HEMTs are based on a heterostructures comprising GaN and AlGaN. One difficulty with group III nitrides is the lattice mismatch and resulting lattice strain which deteriorates the device performance and longevity.
The most important physical device dimension which governs the breakdown voltage in Group III nitride HEMTs is the gate-drain spacing LGD where most of the voltage drops in the pinch-off device condition. The challenge of achieving high breakdown voltage VBR with a minimum on-resistance RON translates into an optimal field profile in the gate-drain region so that it is able to sustain the highest possible voltage at the lowest LGD value.
An ideal switching will block infinite voltage when OFF and pass infinite current when ON with no voltage drop across it. In other words, the switch has zero resistance when ON and infinite resistance when OFF. In reality, an ideal switch performance can never be achieved by a practical power semiconductor switch. However, the aim of the power semiconductor have been to achieve a device with as low as a resistance as possible when in ON state called “ON resistance” (RON) of the device for the given maximum voltage it can block in OFF state know as “breakdown voltage” (VBR) of the device.
Another major factor that limits the performance and reliability of III-nitride HEMT technology for high frequency, high power and high breakdown voltage applications is their relatively high gate leakage currents. The gate leakage reduces the breakdown voltage. It also reduces the power added efficiency and increases the noise to signal ratio.
Initially AlGaN/GaN HEMTs have faced many problems in solving these issues. One of the solutions was to make insulated gate devices which have gate-leakage currents which are several orders lower than Schottky-gate HEMTs. This makes them attractive candidates as a building block for the AlGaN based power converters. However, the associated processes may not be available for low cost and high yield manufacture.
Ternary and quaternary group III nitrides comprising indium have attracted much attention due to the possibility of improved lattice matching with gallium nitride. Implementation of these materials has been complicated by the large band offsets and abrupt changes in properties including band gap, refractive index and chemical reactivity at the interface between AlInN and GaN. Near lattice matched AlInN/GaN heterostructures have been demonstrated for use in AlInN Bragg reflectors, microcavities and transistors.
AlInN alloys have been considered to be candidates for optoelectronic devices covering an extremely wide spectral range from deep UV to infrared due to the large band gap range of 6.2 eV for AlN to 0.7 eV for InN. Unfortunately, growth of AlInN over the full compositional range has been thwarted by problems associated with phase separation during epitaxial growth due, in part, to the large disparity in cation sizes and the differences in thermal properties of the binary constituents. Because of this lattice matching of Al0.83In0.17N/GaN, the heterostructure interface minimizes strain which minimizes cracking and/or dislocation formation.
In replacing AlGaN barrier layer with AlInN, HEMTs in turn offer higher sheet charge densities because of the higher spontaneous polarization of AlInN compared with AlGaN.
There has been a long felt need in the art for improved semiconductor structures based on group III nitrides. However, the difficulties associated with the materials have limited the opportunities.